1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to systems and methods for implementing double wide channels in a communication system.
2. Description of the Related Art
As described in U.S. Pat. No. 6,016,311, titled “Adaptive time division duplexing method and apparatus for dynamic bandwidth allocation within a wireless communication system,” which is hereby incorporated by reference in its entirety, a wireless communication system facilitates two-way communication between a plurality of subscriber radio stations and a base station, where the base station is configured to communicate with multiple devices and is coupled to a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (“PCS”), and cordless telephones. One objective of these wireless communication systems is to provide communication channels on demand between the plurality of subscriber units and their respective base stations in order to connect a subscriber unit user with the fixed network infrastructure (usually a wire-line system). In wireless systems having multiple access schemes, a time “frame” is often used as the basic information transmission unit, where each frame is sub-divided into a plurality of time slots, where some time slots may be used for control purposes and some for information transfer. Subscriber units typically communicate with a selected base station using a “duplexing” scheme that allows information to be exchanged in both directions.
Transmissions from the base station to the subscriber unit are commonly referred to as “downlink” transmissions. Transmissions from the subscriber unit to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, the prior art wireless communication systems have typically used either time division duplexing (“TDD”) or frequency division duplexing (“FDD”) methods to facilitate the exchange of information between the base station and the subscriber units. Both TDD and FDD systems of duplexing are known in the art.
Recently, wideband or “broadband” wireless communications networks have been proposed for delivery of enhanced broadband services such as voice, data and video. Broadband wireless communication systems typically facilitate two-way communication between a plurality of base stations and a plurality of fixed subscriber stations or Customer Premises Equipment (“CPE”). In one embodiment, multiple CPE's are each coupled to a plurality of end user connections, which may include both residential and business customers, where the end user connections of the system may have different and varying usage and bandwidth requirements. Each base station may service several hundred or more residential and business CPE's, and each CPE may service several hundred or more end user connections. An exemplary broadband wireless communication system is described in the incorporated U.S. Pat. No. 6,016,311.
Transmission of data between a base station and CPE's is typically at a particular frequency and within a particular frequency bandwidth, or channel. For example, typical channel bandwidths used in point-to-multi-point and point-to-point systems include 7 MHz, 14 MHz, 25 MHz, 28 MHz, 50 MHz, and 56 MHz. In RF communication systems, transceivers used by base stations and CPE's typically comprise a radio transceiver, or simply a “radio,” that is configured to transmit and receive communication signals within a particular frequency range. The bandwidth of a channel, coupled with the technology used to implement a wireless link using that channel, determines the user data bandwidth available on the channel. For example, a 25 MHz channel with a 0.25 roll-off factor using 64-QAM modulation (described in further detail below) provides a bit rate of 120 Mbps. Typically, forward error correction (“FEC”) is also applied to data signals, thus decreasing the available bandwidth. For example, it would not be uncommon for a FEC to consume 25% of the raw bit rate. In the current example, use of FEC that consumes 25% of the transmitted signal would leave a bit rate of 90 Mbps available for a combination of user traffic, radio link control (RLC), media access control (MAC), and network management. As those of skill in the art will recognize, a rate of 90 Mbps is not sufficient to fully support a single user achieving a peak transfer rate on a 100BaseT Ethernet service. This problem is further evident in situations where a link between a base station and CPE's uses multiple services, such as 100BaseT services, or attempts to provide service to some portion of a Gigabit Ethernet service. Accordingly, there is a need for systems and methods that support transmission of data on wider channels, thus allowing a greater bandwidth of information to be communicated.
Simply designing modems and radios that accommodate larger bandwidth channels is one current approach to this problem. However, this approach can suffer from economies of scale, flexibility, and regulatory requirements. For instance, regulatory requirements often restrict the width of communication channels. Additionally, some systems require smaller channels to maintain compliance or interoperability with certain standards. For example, ETSI BRAN HiperAccess mandates 28 MHz channels for compliance. Building one device (e.g. 28 MHz channels) for one market and another device (e.g., 56 MHz channels) for another market can reduce the ability to take advantage of economies of scale, such as better parts pricing, that may be obtained if the combined total of the devices were identical. For example, in a given geographic location, only a fraction of the CPE's may need, or support, a bandwidth higher than mandated by standards or regulations. According to the prior art, a base station may use two separate systems, one for high bandwidth users and one for low bandwidth users, in order to accommodate the higher bandwidth CPE's.
Because of the above-described deficiencies in the current art, systems and methods for increasing the bandwidth of communication channels while maintaining operability with existing communication systems and standards are desired. Accordingly, a system that provides either two totally independent channels of one bandwidth or a combined channel of double the bandwidth in a single device is desired. Further, it would be advantageous to provide a means to use two regulatory or standards compliant single-bandwidth channels to logically provide user data services with a double bandwidth channel, thus allowing the transport of services which have sustained or peak rates greater that can be accommodated on one single bandwidth channel. In the following description, the term “single-wide” is used in reference to base stations and CPE's that communicate using a communication channel having a predetermined bandwidth, such as a bandwidth that is equal to or less than the relevant standards and regulations, for example. The term “double-wide,” as used herein with reference to base stations and CPE's, indicates that the referenced base stations or CPE's communicate using a communication channel having a bandwidth that is double the “single-wide” bandwidth used for the particular base stations and CPE's. Accordingly, a system that supports single-wide CPE's, as well as double-wide CPE's, is desired. In particular, a system that communicates properly with existing single-wide CPE's without requiring any modifications to the single-wide CPE's, while providing the ability to communicate with double-wide CPE's, is desired.